How do I create a workflow to hide my current menu bar and show a Slideable Menu bar for mobile devices when the page decreases to > 667px?
You can use a Hiding rule and Conditionals.
In my Free App template there is an example (go to link, go to Add to account, and create a new Bubble App using this template to see it in the editor)
Also here is what it looks like to hide an element in the Responsive window…
And here I put a condition on a Group holding the Slideable Menu to show at a certain page width. You could also use the condition to Be Visible when another specific Group is NOT visible